How long is Canada's shoreline?
If you were to try to walk around Canada, following the shoreline at a good pace of 20 kilometres each day, it would take you 33 years to complete the journey. At 243,000 kilometres, Canada's shoreline is the longest in the world.
Of course, to go from the Strait of Juan de Fuca to the Bay of Fundy you would have to walk in and out of the fjords of British Columbia, along the frozen tundra of the Yukon and Northwest Territories not to mention across pack ice to take in the myriad Arctic Islands, back through the Fjords of Labrador, and in and out of every little fishing cove in Atlantic Canada. Along the way you would border three oceans and see many different kinds of coastline.
Images of Canada's coastline
Some of our coasts are dominated by hard bedrock that forms towering cliffs and rocky shorelines. Other areas have lower cliffs made of sand, gravel and mud. You would walk along sand beaches, cobble beaches and mud flats. You would have to struggle across marshes, sand dunes and river deltas. It may well take you longer than 33 years.
Why is our coastline so important?
Every year, Canadians invest about $1 billion on projects related to our coasts. The funds are used to maintain ports and harbours, for erosion protection, pollution control and aquaculture, and for recreation facilities. A valuable investment when you consider that about one-third of Canada's Gross National Product (GNP) is generated by activities that in one way or another use the coastline either directly or as a transportation route.
Beyond that, our coasts provide important habitats to hundreds of species of birds and wildlife. Some of the world's largest natural wetlands, such as the MacKenzie Delta and Hudson Bay, are found in Canada's coastal regions.
These are some of the factors that explain why the Geological Survey of Canada (GSC) is so interested in studying our coastline and the many processes that affect it. Scientists are trying to understand the causes and rates of erosion, and how sediment is transported and deposited within the coastal zone, and what can be done to manage this natural resource.
What is erosion?
Erosion is the process by which material is removed from cliffs and beaches, causing the coastline to retreat inland. It is a natural process that provides sediment for building other coastal features. Waves and currents transport the mud, sand and gravel alongshore to adjacent shores such as spits and barrier islands, offshore, into basins and seabeds or into estuaries and bays, thereby resupplying and maintaining marshes. Erosion is a very important process in the evolution of coastal landscapes.
However for people, erosion can be a hazard. If a shoreline continues to erode or if homes, businesses and public buildings are situated too close to the present shoreline they can be undermined by erosion. At times, especially during severe storms, erosion can even damage wharves, sea walls and breakwaters that were built to protect coastal communities.
What causes erosion?
Many factors cause erosion, and they vary from place to place around the country. In most regions, the pounding of the waves on the shoreline, during storms, is an important cause. Waves attack at the base and transport the eroded material away, exposing deeper sections of the cliff to erosion. If there is insufficient sediment to replace the material carried away from a shoreline, the shore will retreat or change shape so that it can better maintain its position against natural processes such as wave action. Storm waves cause erosion of sand and gravel from beaches, but material is often returned to the beach during fair weather.
In the Arctic, the sea is frozen for most of the year, meaning that waves are not usually a factor. But movement of the ice itself can scrape the coast, causing erosion. Also, where the Arctic ground is frozen, cliffs can be eroded by the melting of the permafrost and result in slumping of the shoreline. Sea ice impacts are also observed along parts of southern Canada such as the Gulf of St Lawrence to Great Lakes. Sea ice can damage infrastructure when it is forced onshore by winds during spring breakup or when the ice is more mobile.
Another important cause of erosion is a rise in sea level which exposes new land to wave attack. If insufficient new sediment is added to the coast during a rise in the sea level, the rate of inland retreat will likely increase.
What causes the sea level to rise?
The short answer is "ice", but it has caused two quite different effects, both of which are visible on Canada's coasts. More than 10,000 years ago, the world was largely under the influence of an Ice Age. Much of the northern hemisphere was covered by ice, kilometres thick. The ice had formed from water from the world's oceans, and in the process, the level of the oceans had dropped by more than 100 metres. As the Ice Age came to an end and the ice began to melt, the water was returned to the oceans which again began to rise. (Read more about changing sea levels in Atlantic Canada) To a small extent, this process is still happening, and can be perceived in areas such as Nova Scotia. In Canada, where much of the ice was to be found during the Ice Age, another factor is important. The weight of the ice on the Earth's crust; with the weight now removed, the land is rebounding to its original position. Examples of the resulting terraced coastlines can be found in the Arctic, where the rebounding makes the sea level appear to be dropping, instead of rising. There is one further factor to be considered because we are adding large volumes of carbon dioxide and other gases into the atmosphere, scientists estimate that it is beginning to heat up faster as a result of the greenhouse effect. The warming effect may be accelerating the melting rate of the remaining ice caps in Greenland and the Antarctic. In addition warm water takes up more room than cold water so as the oceans warm they expand. The prediction is that the sea will start to rise at a faster rate over the next century, and that many areas of Canada and the rest of the world will be subjected to accelerated rates of coastal change.
How fast is our coastline retreating?
First, we must remember that not all parts of the country are experiencing rising sea level. Most of the eastern Arctic, Quebec and Newfoundland and Labrador are, in fact, experiencing a falling sea level, and erosion is less likely to occur in these regions. In the remainder of the Atlantic region, including most of Nova Scotia, the sea level is rising. It is also rising in the Beaufort Sea, off the Yukon and Northwest Territories. In both regions, GSC scientists have been monitoring selected shorelines to measure the effect of waves, currents, winds, and sea ice, and the rates at which different types of shores respond to different processes. For example, recent monitoring of two beaches on the Eastern Shore of Nova Scotia has shown the differences in coastal change: one low pebble-cobble beach migrated 100m landward between 1996 and 2006, whereas a higher pebble-cobble beach a few kilometres away shows little retreat.
Obviously, in areas where the coastline is rocky the rate of retreat is barely noticeable over historical time. In other areas, where the coast is composed of loose sand, gravel and mud, the rate of retreat is much higher. In Atlantic Canada, rates of erosion can reach up to 10 metres per year, but are generally less than one metre per year. Historical records show the loss of entire islands along the coast of Nova Scotia. Along the Beaufort Sea, the average rate of retreat is generally a little higher, being between one and two metres per year.
Can coastal erosion be prevented?
Coastal protection can be a very expensive business because of cost of materials construction and ongoing maintenance as sea levels rise. But it can be done in order to protect important installations such as hospitals and other institutions, ports, and major highways. In many cases where this has been tried in the past, the protection has proven less than adequate. With the increased risk of coastal erosion posed by greenhouse warming, there is a greater need than ever for Canada to understand, adapt and manage the development of our coastlines.
Pressures of conflicting land use are expected to increase over the coming years. In order to allow for better design of structures and more responsible management of the coastal zone, it is necessary to understand the geological and oceanographic processes operating on them. Understanding the physical framework and the response of a particular coast to natural processes will help prevent costly errors in planning and locating structures and facilities in the coastal zone, and reduce their vulnerability to erosion.